The term “expandable beads based on vinyl aromatic polymers” as used in the present description and claims, means vinyl aromatic polymers in the form of granules, containing an expanding system and other additives.
These expandable thermoplastic polymers in the form of granules are particularly used, after expansion and moulding, in the production of household appliances or other industrial equipment, in packaging and thermal insulation in the building industry, due to their thermo-insulating properties. Thermoplastic vinyl aromatic polymers such as polystyrene can be made expandable by incorporating an expandable agent in the polymeric matrix. Typical expanding agents for vinyl aromatic polymers include at least one liquid hydrocarbon containing from 3 to 7 carbon atoms, a halogenated hydrocarbon, carbon dioxide or water. The quantity of expanding agent usually ranges from 2 to 15% by weight. Expandable polymers are produced in general as beads or granules which, under the action of heat, supplied, for example, by steam, are first expanded until a desired density is reached and, after a certain aging period, are sintered in closed moulds to produce blocks or the desired final products.
The making of such expandable beads has already been described in EP 126459, US 2006 211780, US 2005 156344, U.S. Pat. No. 6,783,710 and WO 2008 141766.
The production of beads of PS incorporating pentane is difficult due to the balance required between ease of extrusion/granulation and foam process and compression resistance of the blocks made with the sintered expanded beads (the insulation boards etc. . . . ).
EP 372343 A1 at page 12 describes EPS comprising carbon black 0, 4, and 10 weight percent and talc: 0 to 0.20 weight percent. It is mentioned that the use of 10% carbon black reduces the thermal conductivity by 15%.
WO 97 45477 A1 describes an EPS comprising 2-8% carbon black having an area ranging from 10 to 500 m2/g. In examples 4 and 5 for 6 w % carbon black the thermal conductivity λ is 30-33 mW/m° K. There is no talc.
EP 620 246 B1 describes moulding comprising expanded polystyrene foam and an athermanous material, where the expanded polystyrene foam has a density of less than 20 kg/m3 and the athermanous material absorbs infrared radiation. In an example for 2 w % carbon black and a foam density of 10 kg/m3 the thermal conductivity λ is 35 mW/m° K. There is no talc.
WO 2004-087798 A1 relates to expandable vinylaromatic polymers which comprise:
a) a matrix obtained by polymerizing 50-100% by weight of one or more vinylaromatic monomers and 0-50% by weight of a copolymerizable monomer; b) 1-10% by weight, calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix;c) 0.01-20% by weight, calculated with respect to the polymer (a), of carbon black homogeneously distributed in the polymeric matrix having an average diameter ranging from 30 to 2000 nm, a surface area ranging from 5 to 40 m2/g, a sulfur content ranging from 0.1 to 2000 ppm and an ash content ranging from 0.001 to 1%. In an example for 1 w % carbon black the thermal conductivity λ is 36.5 mW/m° K. There is no talc.
WO 2006-058733 A1 relates to expandable styrene polymer granulates, which contain
a) between 5 and 50 wt. % of a filler, selected from pulverulent inorganic materials such as talc, chalk, kaolin, aluminium hydroxide, aluminium nitrite, aluminium silicate, barium sulphate, calcium carbonate, titanium dioxide, calcium sulphate, silicic acid, quartz powder, aerosil, alumina or wollastonite andb) between 0.1 and 10 wt. % carbon black or graphite.In example 2 there are 1 w % carbon black and 10 w % chalk, the thermal conductivity λ is 32 mW/m° K.
WO 2006 108672 A2 describes a process for improving the insulating capacity of expanded vinyl aromatic which comprises:
1) preparing beads of expandable vinyl aromatic polymers containing 1-10% by weight, calculated with respect to the polymer, of an expanding agent englobed in the polymeric matrix and 0.001-25% by weight, calculated with respect to the polymer (a), of an athermanous additive comprising carbon black homogeneously distributed in the polymeric matrix;2) treating the surface of the beads, before deposition of the coating, with a liquid lubricating agent; and3) thermally treating the beads with hot air at a temperature ranging from 30 to 60° C.
In an example for 1 w % carbon black the thermal conductivity λ is 35.2 mW/m° K. In an example for 1 w % carbon black the thermal conductivity λ is 33 mW/m° K. In an example for 1 w % carbon black+1 w % graphite the thermal conductivity λ is 32 mW/m° K. There is no talc.
US 2007 0112082 A1 relates to a moldable-foam molding with a density from 8 to 200 g/l, obtainable via fusion of prefoamed foam beads comprising expandable pelletized thermoplastic polymer materials, wherein the pelletized polymer materials comprise from 1 to 50% by weight, of one or more fillers selected from the group consisting of talc, chalk, kaolin, aluminum hydroxide, magnesium hydroxide, aluminum nitrite, aluminum silicate, calcium carbonate, calcium sulfate, silica, powdered quartz, Aerosil, alumina and glass beads. In an embodiment the moldable foam molding further comprises from 0.1 to 10% by weight of carbon black or graphite. In an example for 1 w % carbon black and 10 w % chalk, a foam density of 18.8 kg/m3 the thermal conductivity λ is 35.2 mW/m° K.
WO 2007 045454 A1 relates to expandable granulates, having compositions based on vinyl-aromatic polymers, essentially consisting of:
a) 65-99.8% by weight of a copolymer obtained by polymerizing 85-100% by weight of one or more vinyl-aromatic monomers having general formula (I) and 0-15% by weight of an a-alkylstyrene in which the alkyl group contains from 1 to 4 carbon atoms;
b) 0-25% by weight, calculated with respect to the polymer (a), of a carbon black having an average diameter ranging from 10 to 1000 nm and a surface area ranging from 5 to 200 m2/g;
c) at least one of the following additives (cl)-(c3): ci) 0.01-5% by weight, calculated with respect to the polymer (a), of graphite having an average diameter ranging from 0.5 to 50 μm; c2) 0.01-5% by weight, calculated with respect to the polymer (a), of oxides and/or sulfates and/or lamellar dichalcogenides of metals of groups hA, IIIA, IIB, IyE, VIE or VIIIB, c3) 0.01-5% by weight, calculated with respect to the polymer (a), of inorganic derivatives of silicon of the lamellar type;d) 0-5% by weight, calculated with respect to the polymer (a), of a nucleating agent; ande) 1-6% by weight, calculated with respect to 100 parts of the total of (a)-(d), of one or more expanding agents.
In an example there is 4 w % of carbon black. There is no talc and no thermal conductivity is cited.
WO 2008 141766 A1 relates to a process to make EPS. In the examples at table 2 there is 5.2% of graphite or 4.7% of talc. There are no examples in which talc and graphite or carbon black are simultaneously present.
WO 2008 061678 A2 relates to expandable vinyl aromatic polymers which comprise:
a) a matrix obtained by polymerizing 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of at least one copolymerizable monomer;
b) 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix;
c) 0.01-20% by weight, calculated with respect to the polymer (a), of a filler including carbon black electrically conductive and homogeneously distributed in the polymeric matrix, with a surface area, measured according to ASTM D-3037189, ranging from 5 to 200 m2/g.
In the examples for 1 to 4 w % carbon black, a foam density of 17 kg/m3 the thermal conductivity λ is ranging from 31 to 33.3 mW/m° K. In an example for 1 w % carbon black and 0.2 w % graphite, a foam density of 18.3 kg/m3 the thermal conductivity λ is 30.1 mW/m° K. There is no talc.
It has now been discovered that by selecting a talc having a mean diameter above about 8 μm, said mean diameter being measured by Laser Mastersizer according to standard ISO 13320-1, the proportion of carbon black can be lowered. Simultaneously the 10% compression strength is maintained over a wide range of foam density.